6 Meter Converters

I know 6 meters is not a popular band, but it is fun to scan the band and some signals are present. I posted this due to a 6 meter converter post of various 6 meter converters was never posted on AMfone.
Most vintage receivers do not cover 6 meters and if so the receiver cannot compete with a low noise high gain converter. Three converters are available from time to time on Ham sites and eBay. If you know of other converters, please comment.

Ameco CN-50
This is a sensitive low noise converter using three nuvistor (two preamp, one mixer) and a 6J6 osc/multiplier. The conversion is across the ham bands from 7mHz to 11mHz to 28mHz to 32mHz for 50mHz to 54mhz depending upon the crystal used. For Ham band only receivers the 28mHz to 30mHz can cover 50mHz to 52mHz. I found specs in a Lafayette catalog here:
'Extremely sensitive converters employing
3 Nuvistors for minimal noise. Average
gain is 50 db with noise figure of 2.5
db at 50 Mc. Spurious rejection more than 70 db'.
I doubt 50dB gain as the Ameco PLC-P Cascade nuvistor preamp (same two preamp tubes as CN-50) is rated at 20+dB gain. 20dB gain it certainly is high enough. Bama archive shows the crystal conversion frequencies; The converter does not have a built-in power supply.

Filter King VHF-50
The VHF-50 is specified at 4dB noise and 20dB gain. 4dB is low noise. It uses three 6BH8 tubes. It is specified to convert to 30mHz to 34mHz. Some general coverage receivers have this frequency range. Bama archive has the manual and schematic. The converter does not have a built-in power supply.

Lafayette HE-56
I cannot find a schematic for the converter, but found this in a Lafayette 1964 catalog:
'A deluxe 6-meter converter designed to respond to the
weakest signals with very low noise. The HE-56 will
convert any shortwave receiver that tunes 7-11 Mc
to cover 50-54 Mc. Easy to install between main
antenna and receiver's antenna terminals When the
converter's control switch is in the OFF position.
signals from the main antenna will be fed around
the converter circuit into the receiver thus the receiver will receive both the original frequencies and
the 6-meter band. Rugged printed circuit and heavy
gauge steel chassis make this unit as durable as the
receiver it's connected to. SPECS: Freq. range -50-54
Mc. Crystal frequency is 43 Mc. Sensitivity is better than 1
microvolt for 10 db ratio. Image Rejection is in
excess of 40 db. Antenna input impedance is 52 ohms.
Tubes: 6AQ8. 6BL8'.
I guess the HE-56 has 10dB gain. The HE-56 has a built-in power supply and antenna switch for two separate antennas with SO-239 connectors plus RCA jack on the converter output. I tested this converter and works ok. Less gain than the Filter King and Ameco that are preferred for weak signals. (Listed for sale here).

The Ameco and Filter King need a power supply that is not usually found with the converter. Building a power supply is simple and Antek Transformer sells 25va rated transformers for $13 each. One Antek AN-0206 providing 6.3 volts for filament and another Antek AN-0240 providing 40 volts per winding with two windings in series for 80 volts (B+) into a voltage doubler that will produce about 220 volts. Use a 0B2 regulator tube for the Ameco and a 0A2 regulator tube for the Filter King with proper dropping resistor. I used 3K @ 10 watt dropping resistor for the 0A2 and Antek 40 volt transformer with windings in series for 80 volts. Use a .1uF poly type capacitor (not larger value) on regulator tube output to remove tube operating noise. (An Antek AN-0232 can be used for the lower voltage 0B2 tube). Most regulator tubes have internal jumper wires inside, use the jumper to remove B+ voltage to converter when the tube is removed to prevent damage to the Ameco nuvistors. The Filter King 6BH8 will not be damaged with the 210 volts B+ but use jumper anyways.

Antenna relay. Instead of swapping out antenna connectors when using the converter, a small 6 volt DC coil DPDT relay can be installed in the converter to automatically switch the antenna. Use a half wave diode and a 100uF to 220uF capacitor to provide the 6 volts DC coil voltage. 180-250 ohm coil use 100uF, 100-150 ohm coil use 180uF and lower than 100 ohm coil use 220uF. The converters have extra connections on the power supply connector. The Filter King had two connectors, one four pin and other 5 pin. The four pin has two pins grounded. Remove one pin ground and use it for the relay coil voltage.

Note- The Lafayette has a built-in power supply, just replace the electrolytic capacitors.